A tidal tail is a thin, elongated region of

star A star is an astronomical object comprising a luminous spheroid of plasma (physics), plasma held together by its gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked ...

s and

interstellar gas In astronomy, the interstellar medium is the matter and radiation that exist in the space between the star systems in a galaxy. This matter includes gas in ionic, atomic, and molecular form, as well as dust and cosmic rays. It fills interstellar s ...

that extends into space from a

galaxy A galaxy is a system of stars, stellar remnants, interstellar gas, dust, dark matter, bound together by gravity. The word is derived from the Greek ' (), literally 'milky', a reference to the Milky Way galaxy that contains the Solar System. ...

. Tidal tails occur as a result of

galactic tide A galactic tide is a tidal force experienced by objects subject to the gravitational field of a galaxy such as the Milky Way. Particular areas of interest concerning galactic tides include galactic collisions, the disruption of dwarf or satellit ...

forces between

interacting galaxies Interacting galaxies (''colliding galaxies'') are galaxies whose gravitational fields result in a disturbance of one another. An example of a minor interaction is a satellite galaxy disturbing the primary galaxy's spiral arms. An example of a ...

. Examples of galaxies with tidal tails include the

Tadpole Galaxy The Tadpole Galaxy, also known as UGC 10214 and Arp 188, is a disrupted barred spiral galaxy located 420 million light-years from Earth in the northern constellation Draco. Its most dramatic feature is a trail of stars about 280,000 light-years ...

and the

Mice Galaxies NGC 4676, or the Mice Galaxies, are two spiral galaxies in the constellation Coma Berenices. About 290 million light-years distant, they have begun the process of colliding and merging. Their name refers to the long tails produced by tidal acti ...

. Tidal forces can eject a significant amount of a galaxy's gas into the tail; within the

Antennae Galaxies The Antennae Galaxies (also known as NGC 4038/NGC 4039 or Caldwell 60/Caldwell 61) are a pair of interacting galaxy, interacting galaxies in the constellation Corvus (constellation), Corvus. They are currently going through a Starburst Galaxies, ...

, for example, nearly half of the observed gaseous matter is found within the tail structures. Within those galaxies which have tidal tails, approximately 10% of the galaxy's stellar formation takes place in the tail. Overall, roughly 1% of all stellar formation in the known universe occurs within tidal tails. Some interacting galaxy pairs have two distinct tails, as is the case for the Antennae Galaxies, while other systems have only one tail. Most tidal tails are slightly curved due to the rotation of the host galaxies. Those that are straight may actually be curved but still appear to be straight if they are being viewed edge-on.

History

The phenomena now referred to as tidal tails were first studied extensively by

Fritz Zwicky Fritz Zwicky (; ; February 14, 1898 – February 8, 1974) was a Swiss astronomer. He worked most of his life at the California Institute of Technology in the United States of America, where he made many important contributions in theoretical and ...

in 1953. Several astrophysicists expressed their doubts that these extensions could occur solely as the result of tidal forces, including Zwicky himself, who described his own views as "unorthodox".

Boris Vorontsov-Velyaminov Boris Aleksandrovich Vorontsov-Velyaminov (russian: Борис Александрович Воронцов-Вельяминов; February 14, 1904 – January 27, 1994) was a Russian astrophysicist. His name is sometimes given as Vorontsov-Ve ...

argued that the tails were too thin and too long (sometimes as large as 100,000

parsec The parsec (symbol: pc) is a unit of length used to measure the large distances to astronomical objects outside the Solar System, approximately equal to or (au), i.e. . The parsec unit is obtained by the use of parallax and trigonometry, and ...

s) to have been produced by gravity alone, as gravity should instead produce broad distortions. However, in 1972, renowned astronomer

Alar Toomre Alar Toomre (born 5 February 1937, in Rakvere) is an American astronomer and mathematician. He is a professor of applied mathematics at the Massachusetts Institute of Technology. Toomre's research is focused on the dynamics of galaxies. He is a ...

proved that it was indeed tidal forces that were responsible for the tails.

Gallery

Galaxy with an ejected supermassive black hole.jpg, Arc-shaped tidal tails in galaxy 3C186.

Notes

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